I purchased my betta, sulu, at petco a little while ago and have now been treating him for fin and tail rot for about 3 weeks. He was labeled as a female and was not in very good condition. For the time he has been with me he has been living in a one gallon tank with daily 100% water changes to help heal him. For the first seven or so days I used aquarium salt. I also have a 10 gallon tank that I have been cycling in order for Sulu to have a bigger and better home. It is almost finished cycling (yay!). Ideally, I would like to have him live with a school of Tetras, and I would add him to the tank last. My concern is that the move will be stressful for him, Should I wait until he is fully healed from the fin rot or should I move him in once the rest of the inhabitants are added and simply clean the tank regularly? There are live plants and more hiding places, so I think that will be a better environment for him, but I'm just not sure.
Here's are some pictures of him. He's been recovering and regrowing but he still looks to be in rough shape and his fins are quite red.

I would be careful with tetras they can hurt betta find or Betta can hurt them so you would need be careful to not hurt them and fin rot is hard to catch except in bad water for most tetras you need 6 and that might be way to many for a 10 gallon but with medicine and aquarium salt treatment he will recover soon so probably wait till fully healthy.

Thanks, yeah I recognize that a school of tetras is a lot of a ten gallon. Ideally, I would like to put them in there, but I am putting the needs of my betta first as that was who the tank was intended for.

I'm going through the same thing basically, waiting on 10G to cycle while healing fin rot. I put Mista in a 1G, hoping that the absence of current and the inability to constantly swim would help him heal faster but I felt the daily 100% were too much stress for him, he just wasn't himself. Decided to go back to the 5.5G, cleaned it well, took out the carbon filter, put him in there with AQ salt and he's already doing much better.

I would say wait. I'm not sure if you can contaminate a new tank or not, maybe someone has that info, but I feel its better to be safe! Keep an eye on the black parts, that's where the rot is and the clear parts are new growth. I hope for the best with you and Sulu! :0)

Yeah I feel like the stress of being constantly changed may stress him, but I don't know that I'm ready to move him. I will keep up for the changes and hope for the best. Thanks for your help and good wishes!